[Concurrency] Actors & actor isolation

[Lantua]

@ktoso

The rule is simple: Each actor must execute on its executor, this is how the model achieves thread safety (and sanity). There if the caller, task1 and task2 are on different actors, there would be hops back and forth, yes — that’s semantically what was asked for by such code. If they’re all the same actor, there’s no hops.

These hops can sometimes be optimized away, under special circumstances, but semantically think about it the way as phrased above.

(hopped from the other thread, if you know what I mean )

The code in question:

@MainActor
func foo() async {
  let a = await task1()
  let b = await task2()
}

Is there a case where it wouldn't be optimized? Since we could hop directy from

Task1Actor -> Task2Actor

instead of

Task1Actor -> MainActor -> Task2Actor

There will definitely be some changes in ordering, but I don't yet see where that could be a problem.